The present invention relates to a black composite iron oxide pigment, and a paint and a resin composition using the black composite iron oxide pigment, and more particularly, to a black composite iron oxide pigment capable of exhibiting not only a deep black color, but also excellent acid resistance and light resistance, a paint containing the black composite iron oxide pigment, and a resin composition containing the black composite iron oxide pigment.
Carbon black fine particles and magnetite particles are known as typical black pigments, and have been generally used longtime as colorants for paints, printing inks, cosmetics, rubbers, resin compositions or the like.
Among these conventional black pigments, the carbon black fine particles show a most excellent blackness, and coating films or resin compositions using the carbon black fine particles are also excellent in acid resistance. However, since the carbon black fine particles are particles having an average particle size as small as about 0.005 to 0.05 xcexcm, it is difficult to uniformly disperse the carbon black fine particles in vehicles or resin compositions. In addition, the carbon black fine particles are bulky fine particles having a bulk density of about 0.1 g/cm3 and, therefore, are difficult to handle, resulting in deteriorated workability. Further, the carbon black fine particles have hygiene and safety problems such as carcinogenesis.
Specifically, when the carbon black fine particles are used in a larger amount, a higher blackness can be attained. On the other hand, it is more difficult to uniformly disperse such a large amount of the carbon black fine particles in vehicles or resin compositions, resulting in poor workability. Also, the use of a larger amount of the carbon black fine particles is disadvantageous from the viewpoints of hygiene or safety.
The magnetite particles have an appropriate particle size, specifically an average particle size of about 0.08 to 1.0 xcexcm and, therefore, show an excellent dispersibility in vehicles or resin compositions as well as a good handling property. In addition, the magnetite particles are harmless particles. However, the magnetite particles are insufficient in blackness, and coating films or resin compositions using the magnetite particles are also insufficient in acid resistance.
Further, the magnetite particles tend to be magnetically agglomerated together because of inherent magnetism thereof. For this reason, the use of manganese-containing hematite particles as black iron oxide particles having no magnetism have been proposed from the standpoints of improved dispersibility in vehicles or resin compositions. However, the manganese-containing hematite particles are deteriorated in blackness as compared to that of the magnetite particles.
Thus, it has been strongly required to provide black particles capable of not only showing a good blackness similar to or compatible with that of the carbon black fine particles, an excellent dispersibility in vehicles or resin compositions and a good handling property, but also producing a coating film or a resin composition having excellent acid resistance, light resistance and heat resistance.
Also, in recent years, it has been strongly required to provide black particles exhibiting in addition to the above properties, a less reddish and deep black color.
In order to meet these requirements, various methods have been conventionally attempted for producing composite particles from the carbon black fine particles and magnetite particles, thereby obtaining black particles exhibiting excellent combined properties thereof. For example, there are known 1) the method of adding a water dispersion containing carbon black fine particles to a water suspension containing magnetite particles precipitated from an aqueous solution thereof, and then mixing and stirring the mixed dispersion to absorb the carbon black fine particles onto the surface of the magnetite particles (Japanese Patent Publication (KOKOKU) No. 50-13300(1975)); 2) the method of introducing iron-containing sludge in which high-molecular organic materials such as molasses are dissolved, and a carbon black-containing hot gas into a spray reactor at a temperature of 450 to 850xc2x0 C. in order to produce magnetite particles from the iron salt and simultaneously bond carbon black on the surface of the magnetite particles using the molasses as a binding accelerator (Japanese Patent Application Laid-Open (KOAKI) No. 49-48725(1974)); 3) the method of suspending carbon black in an aqueous iron salt solution, and co-precipitating the carbon black and magnetite by adding alkali to the suspension, thereby producing co-precipitated particles coated with carbon black (Japanese Patent Publication (KOKOKU) No. 55-39580(1980)); 4) the method of adhering carbon black, etc., onto the surface of fine plate-shaped particles, and fixing the carbon black, etc., on the surface of the particles using an anionic, cationic or nonionic surfactant and an organofunctional organosilane compound (Japanese Patent Application Laid-Open (KOAKI) Nos. 6-145556(1994) and 7-316458(1995)); or the like.
At present, it has been strongly demanded to provide black particles capable of not only showing a blackness similar to or compatible with that of carbon black fine particles, a less reddish and deep black color and excellent dispersibility in vehicles or resin compositions, but also providing a coating film or a resin composition having excellent acid resistance, light resistance and heat resistance. However, such black particles capable of fulfilling these requirements have not been obtained conventionally.
That is, in the above conventional method 1) described in Japanese Patent Publication (KOKOKU) No. 50-13300(1975), since the carbon black fine particles tend to be desorbed from the surface of the magnetite particles when dispersed in vehicles or resin compositions because of high desorption percentage thereof, it is difficult to uniformly disperse the carbon black fine particles in vehicles or resin compositions. In addition, the obtained paints or resin compositions are not sufficiently improved in blackness.
In the above conventional method 2) described in Japanese Patent Application Laid-Open (KOKAI) No. 49-48725(1974), in order to obtain a high blackness similar to or compatible with that obtained by using carbon black fine particles only, it is necessary to use the carbon black fine particles in as large an amount as about 280 parts by weight based on 100 parts by weight of the magnetite particles.
In the above conventional method 3) described in Japanese Patent Publication (KOKOKU) No. 55-39580(1980), in order to obtain a high blackness similar to or compatible with that of obtained by using carbon black fine particles only, it is also necessary to add the carbon black fine particles in as large an amount as about 100 to 400 parts by weight based on 100 parts by weight of the magnetite particles. In addition, the carbon black fine particles adhered onto the surface of the co-precipitated particles tend to be desorbed therefrom.
In the above conventional method 4) described in Japanese Patent Application Laid-Open (KOKAI) Nos. 6-145556(1994) and 7-316458(1995), the carbon black fine particles tend to be desorbed from the obtained particles. In addition, the particles obtained by this method are not black particles.
Further, in Japanese Patent Application Laid-Open (KOKAI) No. 11-323174(1999), there are described black composite iron-based particles, comprising black iron oxide particles or black iron oxide hydroxide particles, a coating layer formed on the surface of the black iron oxide or iron oxide hydroxide particles comprising organosilane compounds obtainable from alkoxysilanes, and a carbon black coat adhered on the surface of the coating layer. However, as shown in Comparative Examples below, the obtained particles fail to show a deep black color.
As a result of the present inventors"" earnest studies, it has been found that by forming a coating layer comprising at least one organosilicon compound selected from the group consisting of organosilane compounds obtainable from alkoxysilane compounds, and polysiloxanes, on the surface of iron oxide particles, and then adhering an organic blue-based pigment coat on the coating layer, the obtained black composite iron oxide pigment not only can exhibit a blackness similar to or compatible with that of carbon black fine particles, a less reddish and deep black color, excellent dispersibility in vehicles or resin compositions and a good handling property, but also can provide a coating film or a resin composition having excellent acid resistance, light resistance and heat resistance. The present invention has been attained on the basis of the finding.
An object of the present invention is to provide a black composite iron oxide pigment capable of exhibiting a deep black color, and excellent acid resistance and light resistance.
An another object of the present invention is to provide a paint or resin composition containing black composite iron oxide pigment, exhibiting a deep black color, and excellent acid resistance and light resistance.
To accomplish the aims, in a first aspect of the present invention, there is provided a black composite iron oxide pigment comprising composite iron oxide particles having an average particle size of 0.08 to 1.0 xcexcm, comprising:
as core particles iron oxide particles,
a coating formed on surface of said iron oxide particle, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes, and
an organic blue-based pigment coat formed on said coating comprising said organosilicon compound, in an amount of from 1 to 50 parts by weight based on 100 parts by weight of said iron oxide particles.
In a second aspect of the present invention, there is provided a black composite iron oxide pigment comprising composite iron oxide particles having an average particle size of 0.08 to 1.0 xcexcm, comprising:
as core particles iron oxide particles, wherein a coating layer composed of at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon is disposed between the surface of said iron oxide particles and coating layer comprising said organosilicon compound,
a coating formed on surface of said iron oxide particle, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes, and
an organic blue-based pigment coat formed on said coating comprising said organosilicon compound, in an amount of from 1 to 50 parts by weight based on 100 parts by weight of said iron oxide particles.
In a third aspect of the present invention, there is provided a black composite iron oxide pigment comprising composite iron oxide particles having an average particle size of 0.08 to 1.0 xcexcm, comprising:
as core particles iron oxide particles comprising: iron oxide particles,
a coating formed on the surface of said iron oxide particle, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes, and
a carbon black coat formed on at least a part of the surface of said coating layer comprising said organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said iron oxide particles,
a coating formed on surface of said iron oxide particle, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes, and
an organic blue-based pigment coat formed on said coating comprising said organosilicon compound, in an amount of from 1 to 50 parts by weight based on 100 parts by weight of said iron oxide particles.
In a fourth aspect of the present invention, there is provided a black composite iron oxide pigment comprising composite iron oxide particles having an average particle size of 0.08 to 1.0 xcexcm, comprising:
as core particles iron oxide particles comprising:
iron oxide particles, wherein a coating layer composed of at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon is disposed between the surface of said iron oxide particles and coating layer comprising said organosilicon compound,
a coating formed on the surface of said iron oxide particle, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes, and
a carbon black coat formed on at least a part of the surface of said coating layer comprising said organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said iron oxide particles,
a coating formed on surface of said iron oxide particle, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes, and
an organic blue-based pigment coat formed on said coating comprising said organosilicon compound, in an amount of from 1 to 50 parts by weight based on 100 parts by weight of said iron oxide particles.
In a fifth aspect of the present invention, there is provided a paint comprising a paint base material and a black composite iron oxide pigment as defined in any one of the 1st to 4th aspects.
In a sixth aspect of the present invention, there is provided a resin composition tinted with the black composite iron oxide pigment as defined in any one of the 1st to 4th aspects.
In a seventh aspect of the present invention, there is provided a black composite iron oxide pigment comprising composite iron oxide particles having an average particle size of 0.08 to 1.0 xcexcm, a geometrical standard deviation value of the average particle size of not more than 2.0, comprising:
as core particles iron oxide particles,
a coating formed on surface of said iron oxide particle, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes, and
an organic blue-based pigment coat formed on said coating comprising said organosilicon compound, in an amount of from 1 to 50 parts by weight based on 100 parts by weight of said iron oxide particles.
The present invention will now be described in detail below.
First, the black composite iron oxide pigment according to the present invention is described.
The black composite iron oxide pigment according to the present invention, is composed of black composite iron oxide particles, comprising iron oxide particles as core particles, a coating layer formed on the surface of the iron oxide particles comprising at least one organosilicon compound selected from the group consisting of organosilane compounds obtainable from alkoxysilane compounds, and polysiloxanes, and an organic blue-based pigment coat formed onto the coating layer.
As the core particles used in the present invention, there may be exemplified (A) iron oxide particles such as magnetite particles, zinc-containing magnetite particles, hematite particles and manganese-containing hematite particles which contain manganese in an amount of 5 to 40% by weight based on the total weight of the manganese-containing hematite particles; and (B) composite iron oxide particles comprising the above iron oxide particles as core particles, a coating layer formed on the surface of the iron oxide particles, which comprises at least one organosilicon compound selected from the group consisting of organosilane compounds obtainable from alkoxysilane compounds, or polysiloxanes, and a carbon black coat formed on the coating layer (hereinafter referred to merely xe2x80x9ccomposite iron oxide particles precursorxe2x80x9d).
In the consideration of blackness of the obtained black composite iron oxide pigment, the composite iron oxide particles precursor (B) comprising the iron oxide particles, a coating layer formed on the surface of iron oxide particles which comprises at least one organosilicon compound selected from the group consisting of organosilane compounds obtainable from alkoxysilane compounds, or polysiloxanes, and a carbon black coat formed on the coating layer, is preferred.
The iron oxide particles as core particles are first explained.
The iron oxide particles may be of any suitable shape, and may include, for example, granular particles such as spherical particles, granularated particles, octahedral particles, hexahedral particles, polyhedral particles or the like; acicular particles such as needle-like particles, spindle-shaped particles, rice ball-shaped particles or the like; plate-shaped particles; or the like. Among these particles, in the consideration of dispersibility of the obtained black composite iron oxide pigment, the spherical particles and the granular particles are preferably used as the core particles.
In the case of the granular particles such as spherical particles, granularated particles, octahedral particles, hexahedral particles, polyhedral particles or the like, the iron oxide particles have an average particle size of usually 0.078 to 0.98 xcexcm, preferably 0.088 to 0.68 xcexcm, more preferably 0.098 to 0.48 xcexcm.
In the case of the acicular particles such as acicular particles, spindle-shaped particles, rice ball-shaped particles or the like, the iron oxide particles have an average particle size (i.e., average major axis diameter) of usually 0.078 to 0.98 xcexcm, preferably 0.088 to 0.68 xcexcm, more preferably 0.098 to 0.48 xcexcm, and a ratio of average major axis diameter to average minor axis diameter (hereinafter referred to merely as xe2x80x9caspect ratioxe2x80x9d) of usually 2:1 to 20:1, preferably 2:1 to 15:1, more preferably 2:1 to 10:1.
In the case of the plate-shaped particles, the iron oxide particles have an average particle size (i.e., average plate surface diameter) of usually 0.078 to 0.98 xcexcm, preferably 0.088 to 0.68 xcexcm, more preferably 0.098 to 0.48 xcexcm, and a ratio of average plate surface diameter to average thickness (hereinafter referred to merely as xe2x80x9cplate ratioxe2x80x9d) of usually 2:1 to 50:1, preferably 2:1 to 45:1, more preferably 2:1 to 40:1.
When the average particle size of the iron oxide particles is more than 0.98 xcexcm, the obtained black composite iron oxide pigment may be constituted from coarse particles, resulting in poor tinting strength. When the average particle size is less than 0.08 xcexcm, such particles may tend to be agglomerated by the increase of intermolecular force therebetween due to fine particles. As a result, it may become difficult to form a uniform coating layer comprising alkoxysilane compounds or polysiloxanes on the surface of the iron oxide particles, and uniformly adhere an organic blue-based pigment onto the surface of the coating layer.
The iron oxide particles have a geometrical standard deviation value of preferably not more than 2.0, more preferably not more than 1.8, still more preferably not more than 1.6.
When the geometrical standard deviation value is more than 2.0, the iron oxide particles may be prevented from being uniformly dispersed because of the existence of coarse particles therein. As a result, it may become difficult to form a uniform coating layer comprising alkoxysilane compounds or polysiloxanes on the surface of the iron oxide particles, and uniformly adhere an organic blue-based pigment onto the coating layer. The lower limit of the geometrical standard deviation value of the iron oxide particles is 1.01. It may be difficult to industrially produce particles having a geometrical standard deviation value of less than 1.01.
The iron oxide particles have a BET specific surface area value of usually 1 to 200 m2/g, preferably 1.5 to 150 m2/g, more preferably 2.0 to 100 m2/g.
When the BET specific surface area value is less than 1 m2/g, the iron oxide particles may become coarse, or sintering may be caused between the particles, so that the obtained black composite iron oxide pigment also may include coarse particles and, therefore, may be deteriorated in tinting strength. When the BET specific surface area value is more than 200 m2/g, such particles may tend to be agglomerated by the increase of intermolecular force therebetween due to fine particles. As a result, it may become difficult to form a uniform coating layer comprising organosilicon compounds on the surface of the iron oxide particles, and uniformly adhere an organic blue-based pigment onto the coating layer.
As to the hue of the iron oxide particles, the lower limit of L* value thereof is usually 18.0, and the upper limit of L* value thereof is usually about 28.0, preferably about 25.0; the lower limit of a* value thereof is usually more than 0.0, and the upper limit of a* value thereof is usually about 7.0, preferably about 6.0; and the lower limit of b* value thereof is usually about xe2x88x925.0, and the upper limit of b* value thereof is usually about 2.0, preferably about 1.0.
When the L* value is more than 28.0, the lightness of the iron oxide particles may be too high. As a result, it may become difficult to obtain a black composite iron oxide pigment exhibiting a sufficient blackness. When the a* value is more than 7.0, the iron oxide particles show a strongly reddish color. As a result, it becomes difficult to obtain a black composite iron oxide pigment exhibiting a deep black color.
As to the light resistance of the iron oxide particles, the lower limit of xcex94E1* value as described in detail below is usually more than 5.0, and the upper limit of the xcex94E1* value is usually 12.0, preferably 10.0, when measured by the below-mentioned evaluation method.
Next, the composite iron oxide particles precursor (B) comprising the afore-mentioned iron oxide particles as core particles, an organosilicon compound coating layer formed on the surface of each of the iron oxide particles, and a carbon black coat formed on at least a part of the coating layer, is described below.
The composite iron oxide particles precursor comprise:
as core particles the afore-mentioned iron oxide particles having an average major axis diameter of 0.078 to 0.98 xcexcm;
a coating formed on the surface of the iron oxide particles, comprising at least one organosilicon compound selected from the group consisting of:
(1) organosilane compounds obtainable from alkoxysilane compounds, and
(2) polysiloxanes or modified polysiloxanes, and
a carbon black coat formed on at least a part of the surface of the said coating layer comprising the said organosilicon compound, in an amount of 1 to 30 parts by weight based on 100 parts by weight of the said iron oxide particles.
The properties of the iron oxide particles used as the core particles of the composite iron oxide particles precursor are substantially the same as those of the afore-mentioned iron oxide particles.
The coating formed on the surface of the iron oxide particles comprises at least one organosilicon compound selected from the group consisting of (1) organosilane compounds obtainable from alkoxysilane compounds; and (2) polysiloxanes and modified polysiloxanes selected from the group consisting of (2-a) polysiloxanes modified with at least one compound selected from the group consisting of polyethers, polyesters and epoxy compounds (hereinafter referred to merely as xe2x80x9cmodified polysiloxanesxe2x80x9d), and (2-b) polysiloxanes whose molecular terminal is modified with at least one group selected from the group consisting of carboxylic acid groups, alcohol groups and a hydroxyl group (hereinafter referred to merely as xe2x80x9cterminal-modified polysiloxanesxe2x80x9d).
The organosilane compounds (1) may be produced from alkoxysilane compounds represented by the formula (I):
R1aSiX4xe2x88x92axe2x80x83xe2x80x83(I)
wherein R1 is C6H5xe2x80x94, (CH3)2CHCH2xe2x80x94 or n-CbH2b+1xe2x80x94 (wherein b is an integer from 1 to 18); X is CH3Oxe2x80x94 or C2H5Oxe2x80x94; and a is an integer from 0 to 3.
The drying or heat-treatment of the alkoxysilane compounds may be conducted, for example, at a temperature of usually 40 to 150xc2x0 C., preferably 60 to 120xc2x0 C. for usually 10 minutes to 12 hours, preferably 30 minutes to 3 hours.
Specific examples of the alkoxysilane compounds may include methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, isobutyltrimethoxysilane, decyltrimethoxysilane or the like. Among these alkoxysilane compounds, in view of the desorption percentage and the adhering effect of carbon black, methyltriethoxysilane, phenyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane and isobutyltrimethoxysilane are preferred, and methyltriethoxysilane, methyltrimethoxysilane and phenyltriethoxysilane are more preferred.
As the polysiloxanes (2), there may be used those compounds represented by the formula (II): 
wherein R2 is Hxe2x80x94 or CH3xe2x80x94, and d is an integer from 15 to 450.
Among these polysiloxanes, in view of the desorption percentage and the adhering effect of the carbon black, polysiloxanes having methyl hydrogen siloxane units are preferred.
As the modified polysiloxanes (2-a), there may be used:
(a) polysiloxanes modified with polyethers represented by the formula (III): 
xe2x80x83wherein R3 is xe2x80x94(xe2x80x94CH2xe2x80x94)hxe2x80x94; R4 is xe2x80x94(xe2x80x94CH2xe2x80x94)ixe2x80x94CH3; R5 is xe2x80x94OH, xe2x80x94COOH, xe2x80x94CHxe2x95x90CH2, xe2x80x94C(CH3)xe2x95x90CH2 or xe2x80x94(xe2x80x94CH2xe2x80x94)jxe2x80x94CH3; R6 is xe2x80x94(xe2x80x94CH2xe2x80x94)kxe2x80x94CH3; g and h are an integer from 1 to 15; i, j and k are an integer from 0 to 15; e is an integer from 1 to 50; and f is an integer from 1 to 300;
(b) polysiloxanes modified with polyesters represented by the formula (IV): 
xe2x80x83wherein R7, R8 and R9 are xe2x80x94(xe2x80x94CH2xe2x80x94)qxe2x80x94 and may be the same or different; R10 is xe2x80x94OH, xe2x80x94COOH, xe2x80x94CHxe2x95x90CH2, xe2x80x94C(CH3)xe2x95x90CH2 or xe2x80x94(xe2x80x94CH2xe2x80x94)rxe2x80x94CH3; R11 is xe2x80x94(xe2x80x94CH2xe2x80x94)sxe2x80x94CH3; n and q are an integer from 1 to 15; r and s are an integer from 0 to 15; exe2x80x2 is an integer from 1 to 50; and fxe2x80x2 is an integer from 1 to 300;
(c) polysiloxanes modified with epoxy compounds represented by the formula (V): 
xe2x80x83wherein R12 is xe2x80x94(xe2x80x94CH2xe2x80x94)vxe2x80x94; v is an integer from 1 to 15; t is an integer from 1 to 50; and u is an integer from 1 to 300; or a mixture thereof.
Among these modified polysiloxanes (2-a), in view of the desorption percentage and the adhering effect of the carbon black, the polysiloxanes modified with the polyethers represented by the formula (III), are preferred.
As the terminal-modified polysiloxanes (2-b), there may be used those represented by the formula (VI): 
wherein R13 and R14 are xe2x80x94OH, R16OH or R17COOH and may be the same or different; R15 is xe2x80x94CH3 or xe2x80x94C6H5; R16 and R17 are xe2x80x94(xe2x80x94CH2xe2x80x94)yxe2x80x94; y is an integer from 1 to 15; w is an integer from 1 to 200; and x is an integer from 0 to 100.
Among these terminal-modified polysiloxanes, in view of the desorption percentage and the adhering effect of the carbon black, the polysiloxanes whose terminals are modified with carboxylic acid groups are preferred.
The coating amount of the organosilicon compounds is usually 0.02 to 5.0% by weight, preferably 0.03 to 4.0% by weight, more preferably 0.05 to 3.0% by weight (calculated as Si) based on the weight of the iron oxide particles coated with the organosilicon compounds.
When the coating amount of the organosilicon compounds is less than 0.02% by weight, it may be difficult to adhere the carbon black in a predetermined.
When the coating amount of the organosilicon compounds is more than 5.0% by weight, the carbon black can be adhered in a predetermined. Therefore, it is unnecessary and meaningless to coat the iron oxide particles with such a large amount of the organosilicon compounds.
The amount of the carbon black coat formed is 1 to 30 parts by weight based on 100 parts by weight of the iron oxide particles as core particles.
When the amount of the carbon black coat formed is less than 1 part by weight, the amount of the carbon black may be insufficient, so that it may become difficult to obtain composite iron oxide particles precursor a more excellent blackness.
On the other hand, when the amount of the carbon black coat formed is 1 to 30 parts by weight, the obtained composite iron oxide particles precursor can show a more excellent blackness.
The thickness of carbon black coat formed is preferably not more than 0.04 xcexcm, more preferably not more than 0.03 xcexcm, still more preferably not more than 0.02 xcexcm. The lower limit thereof is more preferably 0.0001 xcexcm.
The carbon black may be adhered either over a whole surface of the coating layer composed of the alkoxysilane or polysiloxanes, or on at least a part of the surface of the coating layer so as to expose a part of the coating layer composed of the alkoxysilane or polysiloxanes to the outer surface of each composite iron oxide particle precursor so that a carbon black coat is formed on the surface of the coating layer. Even though a part of the coating layer composed of the alkoxysilane or polysiloxanes is exposed to the outer surface of each composite iron oxide particle precursor, it is possible to suitably adhere the organic blue-based pigment thereonto.
The particle shape and particle size of the composite iron oxide particles precursor used in the present invention are considerably varied depending upon those of the iron oxide particles as core particles. The composite iron oxide particles precursor have a similar particle shape to that of the iron oxide particles as core particle, and a slightly larger particle size than that of the iron oxide particles as core particles.
More specifically, the composite iron oxide particles precursor (B) used as the core particles in the present invention, have an average particle size as follows.
In the case of the granular particles such as spherical particles, granularated particles, octahedral particles, hexahedral particles, polyhedral particles or the like, the composite iron oxide particles precursor has an average particle size of usually 0.078 to 0.98 xcexcm, preferably 0.088 to 0.68 xcexcm, more preferably 0.098 to 0.48 xcexcm.
In the case of the acicular particles such as needle-like particles, spindle-shaped particles, rice ball-shaped particles or the like, the composite iron oxide particles precursor has an average particle size (i.e., average major axis diameter) of usually 0.078 to 0.98 xcexcm, preferably 0.088 to 0.68 xcexcm, more preferably 0.098 to 0.48 xcexcm, and a ratio of average major axis diameter to average minor axis diameter (hereinafter referred to merely as xe2x80x9caspect ratioxe2x80x9d) of usually 2:1 to 20:1, preferably 2:1 to 15:1, more preferably 2:1 to 10:1.
In the case of the plate-shaped particles, the composite iron oxide particles precursor has an average particle size (i.e., average plate surface diameter) of usually 0.078 to 0.98 xcexcm, preferably 0.088 to 0.68 xcexcm, more preferably 0.098 to 0.48 xcexcm, and a ratio of average plate surface diameter to average thickness (hereinafter referred to merely as xe2x80x9cplate ratioxe2x80x9d) of usually 2:1 to 50:1, preferably 2:1 to 45:1, more preferably 2:1 to 40:1.
The geometrical standard deviation value of the composite iron oxide particles precursor used as the core particles in the present invention is preferably not more than 2.0, more preferably 1.01 to 1.8, still more preferably 1.01 to 1.6.
The BET specific surface area of the composite iron oxide particles precursor used as the core particles in the present invention, is usually 1 to 200 m2/g, preferably 1 to 150 m2/g, more preferably 2.0 to 100 m2/g.
The lower limit of the L* value of the composite iron oxide particles precursor used as the core particles in the present invention is usually 15.0, and the upper limit thereof is usually 23.5, preferably 23.0; the lower limit of the a* value thereof usually more than 0.0, and the upper limit thereof is usually 7.0, preferably 6.0; and the lower limit of the b* value thereof usually xe2x88x925.0, and the upper limit thereof is usually 2.0, preferably 1.0.
The lower limit of the xc2x7E value of the composite iron oxide particles precursor used as the core particles in the present invention is usually more than 5.0, and the upper limit thereof is usually 12.0, preferably 10.0.
The desorption percentage of the carbon black from the composite iron oxide particles precursor used as the core particles in the present invention is preferably not more than 20% by weight, more preferably not more than 10% by weight (calculated as C).
In the composite iron oxide particles precursor used as the core particles in the present invention, at least a part of the surface of the iron oxide particles may be preliminarily coated with at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon (hereinafter referred to as xe2x80x9chydroxides and/or oxides of aluminum and/or siliconxe2x80x9d), if necessary. In this case, the obtained composite iron oxide particles precursor wherein the coating layer composed of hydroxides and/or oxides of aluminum and/or silicon is disposed between the surface of said iron oxide particles and the coating layer comprising said organosilicon compound, can more effectively prevent the organic blue-based pigment adhered thereonto from being desorbed therefrom as compared to the case where the composite iron oxide particles precursor wherein the iron oxide particles are uncoated with hydroxides and/or oxides of aluminum and/or silicon.
The amount of the hydroxides and/or oxides of aluminum and/or silicon coat is preferably 0.01 to 20% by weight (calculated as Al, SiO2 or a sum of Al and SiO2) based on the weight of the iron oxide particles coated.
The particle size, geometrical standard deviation, BET specific surface area and blackness (L* value), wherein the surface of the iron oxide particle is coated with the hydroxides and/or oxides of aluminum and/or silicon, are substantially the same as those of the composite iron oxide particles precursor wherein the iron oxide particle is uncoated with the hydroxides and/or oxides of aluminum and/or silicon.
The desorption percentage of the organic blue-based pigment can be reduced by forming the coating layer composed of hydroxides and/or oxides of aluminum and/or silicon thereon, and is preferably not more than 12%, more preferably not more than 10%.
The composite iron oxide particles precursor (B) used in the present invention can be produced by the following method.
The coating of the iron oxide particles with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes, may be conducted (i) by mechanically mixing and stirring the iron oxide particles together with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes; or (ii) by mechanically mixing and stirring both the components together while spraying the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes onto the iron oxide particles. In these cases, substantially whole amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes added can be applied onto the surfaces of the iron oxide particles.
In order to uniformly coat the surfaces of the iron oxide particles with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes, it is preferred that the iron oxide particles are preliminarily diaggregated by using a pulverizer.
As apparatus (a) for mixing and stirring the iron oxide particles with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes to form the coating layer thereof, and (b) for mixing and stirring carbon black fine particles with the particles whose surfaces are coated with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes to form the carbon black coat, there may be preferably used those apparatus capable of applying a shear force to the particles, more preferably those apparatuses capable of conducting the application of shear force, spatulate-force and compressed-force at the same time. In addition, by conducting the above mixing or stirring treatment (a) of the core particles together with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes, at least a part of the alkoxysilane compounds coated on the iron oxide particles may be changed to the organosilane compounds.
As such apparatuses, there may be exemplified wheel-type kneaders, ball-type kneaders, blade-type kneaders, roll-type kneaders or the like. Among them, wheel-type kneaders are preferred.
Specific examples of the wheel-type kneaders may include an edge runner (equal to a mix muller, a Simpson mill or a sand mill), a multi-mull, a Stotz mill, a wet pan mill, a Conner mill, a ring muller, or the like. Among them, an edge runner, a multi-mull, a Stotz mill, a wet pan mill and a ring muller are preferred, and an edge runner is more preferred. Specific examples of the ball-type kneaders may include a vibrating mill or the like. Specific examples of the blade-type kneaders may include a Henschel mixer, a planetary mixer, a Nawter mixer or the like. Specific examples of the roll-type kneaders may include an extruder or the like.
In order to coat the surfaces of iron oxide particles with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes as uniformly as possible, the conditions of the above mixing or stirring treatment may be appropriately controlled such that the linear load is usually 19.6 to 1960 N/cm (2 to 200 Kg/cm), preferably 98 to 1470 N/cm (10 to 150 Kg/cm), more preferably 147 to 980 N/cm (15 to 100 Kg/cm); and the treating time is usually 5 minutes to 24 hours, preferably 10 minutes to 20 hours. It is preferred to appropriately adjust the stirring speed in the range of usually 2 to 2,000 rpm, preferably 5 to 1,000 rpm, more preferably 10 to 800 rpm.
The amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes added, is preferably 0.15 to 45 parts by weight based on 100 parts by weight of the iron oxide particles. When the amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes is added in an amount of 0.15 to 45 parts by weight, it is possible to adhere 1 to 30 parts by weight of the carbon black onto 100 parts by weight of the iron oxide particles.
Next, the carbon black fine particles are added to the iron oxide particles coated with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes, and the resultant mixture is mixed and stirred to form the carbon black coat on the surfaces of the coating composed of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes added. In addition, by conducting the above mixing or stirring treatment (b) of the carbon black fine particles together with iron oxide particles coated with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes, at least a part of the alkoxysilane compounds coated on the iron oxide particles may be changed to the organosilane compounds.
The obtained particles may be further subjected to drying or heat-treatment, if required, for example, at a temperature of usually 40 to 150xc2x0 C., preferably 60 to 120xc2x0 C. for usually 10 minutes to 12 hours, preferably 30 minutes to 3 hours.
By varying an adding method of the carbon black fine particles, mixing and stirring conditions, and an adhering configuration of the carbon black coat, it is possible to adhere 1 to 30 parts by weight of the carbon black onto the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes coating layer.
In order to form carbon black onto the coating layer composed of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes as uniformly as possible, the conditions of the above mixing or stirring treatment can be appropriately controlled such that the linear load is usually 19.6 to 1960 N/cm (2 to 200 Kg/cm), preferably 98 to 1470 N/cm (10 to 150 Kg/cm), more preferably 147 to 980 N/cm (15 to 100 Kg/cm); and the treating time is usually 5 minutes to 24 hours, preferably 10 minutes to 20 hours. It is preferred to appropriately adjust the stirring speed in the range of usually 2 to 2,000 rpm, preferably 5 to 1,000 rpm, more preferably 10 to 800 rpm.
When the amount of the carbon black fine particles added is more than 30 parts by weight, a sufficient blackness of the resultant composite iron oxide particles precursor can be obtained, but the carbon black tend to be desorbed from the surface of the coating layer because of too large amount of the carbon black adhered, so that it may become difficult to uniformly coat the surface of the composite iron oxide particles precursor with the alkoxysilanes or polysiloxanes, and uniformly adhere the organic blue-based pigment on the surface of the coating layer comprising the alkoxysilanes or polysiloxanes.
At least a part of the surface of the iron oxide particles may be coated with at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon, if required.
The coat of the hydroxides and/or oxides of aluminum and/or silicon may be conducted by adding an aluminum compound, a silicon compound or both the compounds to a water suspension in which the iron oxide particles are dispersed, followed by mixing and stirring, and further adjusting the pH value of the suspension, if required, thereby coating the surfaces of the iron oxide particles with at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon. The thus obtained iron oxide particles coated with the hydroxides and/or oxides of aluminum and/or silicon are then filtered out, washed with water, dried and pulverized. Further, the iron oxide particles coated with the hydroxides and/or oxides of aluminum and/or silicon may be subjected to post-treatments such as deaeration treatment and compaction treatment, if required.
As the aluminum compounds, there may be exemplified aluminum salts such as aluminum acetate, aluminum sulfate, aluminum chloride or aluminum nitrate, alkali aluminates such as sodium aluminate or the like.
The amount of the aluminum compound added is 0.01 to 20% by weight (calculated as Al) based on the weight of the iron oxide particles.
As the silicon compounds, there may be exemplified water glass #3, sodium orthosilicate, sodium metasilicate or the like.
The amount of the silicon compound added is 0.01 to 20% by weight (calculated as SiO2) based on the weight of the iron oxide particles.
In the case where both the aluminum and silicon compounds are used in combination for the coating, the total amount of the aluminum and silicon compounds added is preferably 0.01 to 20% by weight (calculated as a sum of Al and SiO2) based on the weight of the iron oxide particles.
Next, the at least one organosilicon compound selected from the group consisting of organosilane compounds obtainable from alkoxysilane compounds, and polysiloxanes, and the organic blue-based pigment, which are used in the black composite iron oxide pigment of the present invention, will be explained.
The coating layer formed on the surface of the iron oxide particles including the iron oxide particles (A) and the composite iron oxide particles precursor (B) as core particles, comprising the organosilicon compound selected from the group consisting of: (1) organosilane compounds obtainable from alkoxysilane compounds, and (2) polysiloxanes or modified polysiloxanes, is explained.
The organosilane compounds (1) may be produced from alkoxysilane compounds represented by the formula (I):
R1aSiX4xe2x88x92axe2x80x83xe2x80x83(I)
wherein R1 is C6H5xe2x80x94, (CH3)2CHCH2xe2x80x94 or nxe2x80x94CbH2b+1xe2x80x94 (wherein b is an integer from 1 to 18); X is CH3Oxe2x80x94 or C2H5Oxe2x80x94; and a is an integer from 0 to 3.
The drying or heat-treatment of the alkoxysilane compounds may be conducted, for example, at a temperature of usually 40 to 150xc2x0 C., preferably 60 to 120xc2x0 C. for usually 10 minutes to 12 hours, preferably 30 minutes to 3 hours.
Specific examples of the alkoxysilane compounds may include methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, isobutyltrimethoxysilane, decyltrimethoxysilane or the like. Among these alkoxysilane compounds, in view of the desorption percentage and the adhering effect of the organic blue-based pigments, methyltriethoxysilane, phenyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane and isobutyltrimethoxysilane are preferred, and methyltriethoxysilane, methyltrimethoxysilane and phenyltriethoxysilane are more preferred.
As the polysiloxanes (2), there may be used those compounds represented by the formula (II): 
wherein R2 is Hxe2x80x94 or CH3xe2x80x94, and d is an integer from 15 to 450.
Among these polysiloxanes, in view of the desorption percentage and the adhering effect of the organic blue-based pigments, polysiloxanes having methyl hydrogen siloxane units are preferred. p1 As the modified polysiloxanes (2-a), there may be used: (a) polysiloxanes modified with polyethers represented by the formula (III): 
xe2x80x83wherein R3 is xe2x80x94(xe2x80x94CH2xe2x80x94)hxe2x80x94; R4 is xe2x80x94(xe2x80x94CH2xe2x80x94)ixe2x80x94CH3; R5 is xe2x80x94OH, xe2x80x94COOH, xe2x80x94CHxe2x95x90CH2, xe2x80x94C(CH3)xe2x95x90xe2x80x94CH2 or xe2x80x94(xe2x80x94CH2xe2x80x94)jxe2x80x94CH3; R6 is xe2x80x94(xe2x80x94CH2xe2x80x94)kxe2x80x94CH3; g and h are an integer from 1 to 15; i, j and k are an integer from 0 to 15; e is an integer from 1 to 50; and f is an integer from 1 to 300;
(b) polysiloxanes modified with polyesters represented by the formula (IV): 
xe2x80x83wherein R7, R8 and R9 are xe2x80x94(xe2x80x94CH2xe2x80x94)qxe2x80x94 and may be the same or different; R10 is xe2x80x94OH, xe2x80x94COOH, xe2x80x94CHxe2x95x90CH2, xe2x80x94C(CH3)xe2x95x90CH2 or xe2x80x94(xe2x80x94CH2xe2x80x94)rxe2x80x94CH3; R11 is xe2x80x94(xe2x80x94CH2xe2x80x94)sxe2x80x94CH3; n and q are an integer from 1 to 15; r and s are an integer from 0 to 15; exe2x80x2 is an integer from 1 to 50; and fxe2x80x2 is an integer from 1 to 300;
(c) polysiloxanes modified with epoxy compounds represented by the formula (V): 
xe2x80x83wherein R12 is xe2x80x94(xe2x80x94CH2xe2x80x94)vxe2x80x94; v is an integer from 1 to 15; t is an integer from 1 to 50; and u is an integer from 1 to 300; or a mixture thereof.
Among these modified polysiloxanes (2-a), in view of the desorption percentage and the adhering effect of the organic blue-based pigments, the polysiloxanes modified with the polyethers represented by the formula (III), are preferred.
As the terminal-modified polysiloxanes (2-b), there may be used those represented by the formula (VI): 
wherein R13 and R14 are xe2x80x94OH, R16OH or R17COOH and may be the same or different; R15 is xe2x80x94CH3 or xe2x80x94C6H5; R16 and R17 are xe2x80x94(xe2x80x94CH2xe2x80x94)yxe2x80x94; y is an integer from 1 to 15; w is an integer from 1 to 200; and x is an integer from 0 to 100.
In the consideration of adhering effect and desorption percentage of the organic blue-based pigment, the polysiloxanes having methylhydrogensiloxane units, the polysiloxanes modified with polyethers and the polysiloxanes terminal-modified with carboxylic acids, are preferred
The coating amount of the organosilicon compounds is usually 0.02 to 5.0% by weight, preferably 0.03 to 4.0% by weight, more preferably 0.05 to 3.0% by weight (calculated as Si) based on the weight of the core particles coated with the organosilicon compounds.
When the coating amount of the organosilicon compounds is less than 0.02% by weight, it may be difficult to adhere the organic blue-based pigments in a predetermined. When the coating amount of the organosilicon compounds is more than 5.0% by weight, the organic blue-based pigments can be adhered in a predetermined. Therefore, it is unnecessary and meaningless to coat the core particles with such a large amount of the organosilicon compounds.
Examples of the organic blue-based pigments may include phthalocyanine-based pigments such as metal-free phthalocyanine blue, phthalocyanine blue (copper phthalocyanine) and fast sky blue (sulfonated copper phthalocyanine); and alkali blue. In the consideration of acid resistance of the obtained black composite iron oxide pigment, the use of the phthalocyanine-based pigments is preferred.
In particular, in the consideration of the light resistance of the obtained black composite iron oxide pigment, low-chlorinated copper phthalocyanine, NC (non-crystallization)-type copper phthalocyanine and NC-type low-chlorinated copper phthalocyanine are preferably used.
The amount of the organic blue-based pigment adhered is usually 1 to 50 parts by weight, preferably 3 to 45 parts by weight based on 100 parts by weight of the iron oxide particles.
When the amount of the organic blue-based pigment adhered is less than 1 part by weight, the amount of the organic blue-based pigment adhered may be insufficient, so that it may become difficult to obtain a black composite iron oxide pigment having sufficient light resistance and acid resistance as well as an aimed hue.
By adhering 1 to 50 parts by weight of the organic blue-based pigment, the black composite iron oxide pigment showing a deep black color, and excellent light resistance and acid resistance, which is an objective pigment of the present invention, can be obtained
The shape and size of the black composite iron oxide pigment according to the present invention may largely vary depending upon those of the iron oxide particles as core particles. The black composite iron oxide pigment usually has a configuration or shape similar to that of the core particles.
Specifically, in the case where the granular iron oxide particles are used as the core particles, the obtained black composite iron oxide pigment according to the present invention has an average particle size of usually 0.08 to 1.0 xcexcm, preferably 0.09 to 0.7 xcexcm, more preferably 0.1 to 0.5 xcexcm. In the case where the acicular or spindle-shaped iron oxide particles are used as the core particles, the obtained black composite iron oxide pigment has an average particle size (i.e., average major axis diameter) of usually 0.08 to 1.0 xcexcm, preferably 0.09 to 0.7 xcexcm, more preferably 0.1 to 0.5 xcexcm, and an aspect ratio of usually 2:1 to 20:1, preferably 2:1 to 15:1, more preferably 2:1 to 10:1. In the case where the plate-shaped iron oxide particles are used as the core particles, the obtained black composite iron oxide pigment has an average particle size (i.e., average plate surface diameter) of usually 0.08 to 1.0 xcexcm, preferably 0.09 to 0.7 xcexcm, more preferably 0.1 to 0.5 xcexcm, and a plate ratio of usually 2:1 to 50:1, preferably 2:1 to 45:1, more preferably 2:1 to 40:1.
When the average particle size of the black composite iron oxide pigment is less than 0.08 xcexcm, such particles may tend to be agglomerated together by the increase in intermolecular force therebetween due to fine particles, so that it may become difficult to disperse the black composite iron oxide pigment in vehicles or resin compositions. When the average particle size of the black composite iron oxide pigment is more than 1.0 xcexcm, the obtained composite iron oxide pigment may tend to be prevented from being uniformly dispersed in vehicles or resin compositions because of too large particles.
The black composite iron oxide pigment of the present invention has a geometrical standard deviation value of particle sizes of usually not more than 2.0. When the geometrical standard deviation value is more than 2.0, the black composite iron oxide pigment may tend to be prevented from being uniformly dispersed in vehicles or resin compositions because of the existence of coarse particles therein. In the consideration of uniform dispersion in vehicles or resin compositions, the geometrical standard deviation value is preferably not more than 1.8, more preferably not more than 1.6. Further, in the consideration of industrial productivity, the lower limit of the geometrical standard deviation value is 1.01.
The black composite iron oxide pigment of the present invention has a BET specific surface area value of usually 1 to 200 m2/g, preferably 1.5 to 150 m2/g, more preferably 2.0 to 100 m2/g. When the BET specific surface area value of the black composite iron oxide pigment is less than 1 m2/g, the obtained black composite iron oxide pigment may become coarse particles, or sintering may be caused within or between the particles, thereby adversely affecting the dispersibility in vehicles or resin compositions. When the BET specific surface area value of the black composite iron oxide pigment is more than 200 m2/g, such particles may tend to be agglomerated together by the increase in intermolecular force therebetween due to fine particles, resulting in deteriorated dispersibility in vehicles or resin compositions.
As to the hue of the black composite iron oxide pigment according to the present invention, the lower limit of L* value thereof is usually 16.0, and the upper limit of the L* value is usually 23.0, preferably 22.0, more preferably 21.0; the lower limit of the a* value is usually xe2x88x922.0, and the upper limit of a* value thereof is usually 0.0, preferably xe2x88x920.1, more preferably xe2x88x920.2; and the lower limit of b* value thereof is usually xe2x88x926.5, and the upper limit of the b* value is usually 1.5, preferably 1.0.
Among the black composite iron oxide pigments of the present invention, as to the hue of the black composite iron oxide pigments produced by using the composite iron oxide particles precursor as the core particles, the lower limit of L* value thereof is usually 14.5, and the upper limit of the L* value is usually 21.0, preferably 20.0, more preferably 19.0; the lower limit of the a* value is usually xe2x88x922.0, and the upper limit of a* value thereof is usually 0.0, preferably xe2x88x920.1, more preferably xe2x88x920.2; and the lower limit of b* value thereof is usually xe2x88x926.5, and the upper limit of the b* value is usually 1.5, preferably 1.0.
When the L* value is more than 23.0, the lightness of the black composite iron oxide pigment is too high. As a result, the obtained composite iron oxide pigment fails to exhibit an excellent blackness. When the a* value is more than 0.0, the obtain composite iron oxide pigment shows a strongly reddish color. As a result, it may become difficult to obtain a black composite iron oxide pigment exhibiting a deep black color.
The desorption percentage of the organic blue-based pigment from the black composite iron oxide pigment is preferably not more than 20%, more preferably not more than 15%. When the desorption percentage of the organic blue-based pigment is more than 20%, the black composite iron oxide pigment may tend to be inhibited from being uniformly dispersed in vehicles or resin compositions by the desorbed organic blue-based pigment, upon the production of paints or resin compositions.
As to the heat resistance of the black composite iron oxide pigment, the heat-resisting temperature thereof is usually not less than 280xc2x0 C. In particular, in the case where the zinc-containing magnetite particles are used as the core particles, the heat-resisting temperature of the black composite iron oxide pigment is usually not less than 300xc2x0 C. Further, in the case where the hematite particles or the Mn-containing hematite particles are used as the core particles, the heat-resisting temperature of the black composite iron oxide pigment is usually not less than 500xc2x0 C.
As to the light resistance of the black composite iron oxide pigment, the xcex94E1* value thereof is usually not more than 5.0, preferably not more than 4.0 when measured by the below-mentioned evaluation method.
As to the acid resistance of the black composite iron oxide pigment, the xcex94E2* value thereof is usually not more than 1.50, preferably not more than 1.30 when measured by the below-mentioned evaluation method.
In the black composite iron oxide pigment of the present invention, the surface of the iron oxide particles may be previously coated with at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon. The black composite iron oxide pigment produced by using the iron oxide particles coated with the hydroxides and/or oxides of aluminum and/or silicon, can be more effectively prevented from undergoing desorption of organic blue-based pigment from the surface of the iron oxide particles, as compared to those using the iron oxide particles uncoated with the hydroxides and/or oxides of aluminum and/or silicon.
The amount of the hydroxides and/or oxides of aluminum and/or silicon coat is usually 0.01 to 20% by weight (calculated as Al, SiO2 or a sum of Al and SiO2) based on the weight of the iron oxide particles coated with the hydroxides and/or oxides of aluminum and/or silicon coat.
When the amount of the hydroxides and/or oxides of aluminum and/or silicon coat is less than 0.01% by weight, it is difficult to attain the effect of reducing the desorption percentage of organic blue-based pigment. As long as the amount of the hydroxides and/or oxides of aluminum and/or silicon coat lies within the range of 0.01 to 20% by weight, the effect of reducing the desorption percentage of organic blue-based pigment can be sufficiently exhibited. Therefore, it is unnecessary and meaningless to form the hydroxides and/or oxides of aluminum and/or silicon coat in an amount of more than 20% by weight.
The black composite iron oxide pigment using the iron oxide particles wherein the hydroxides and/or oxides of aluminum and/or silicon coat is disposed between the surface of said iron oxide particles and coating layer comprising said organosilicon compound according to the second aspect of the present invention is substantially the same in particle size, geometrical standard deviation value, BET specific surface area value, hue (L* value, a* value and b* value), heat resistance, light resistance xcex94E1* value and acid resistance xcex94E2* value as those of the black composite iron oxide pigment produced by using the iron oxide particles having no hydroxides and/or oxides of aluminum and/or silicon coat as core particles according to the first aspect of the present invention. Thus, the desorption percentage of the organic blue-based pigment from the black composite iron oxide pigment may be improved by forming the hydroxides and/or oxides of aluminum and/or silicon coat on the surface of the iron oxide particles, and is preferably not more than 15%, more preferably not more than 10%.
The black composite iron oxide pigment produced by using the composite iron oxide particles precursor as core particles according to the third aspect of the present invention is substantially the same in particle size, geometrical standard deviation value, BET specific surface area value, hue (a* value and b* value), desorption percentage of organic blue-based pigment, heat resistance, light resistance xcex94E1* value and acid resistance xcex94E2* value as those of the black composite iron oxide pigment using the iron oxide particles as core particles according to the first aspect of the present invention.
The black composite iron oxide pigment produced by using as core particles, the composite iron oxide particles precursor produced from the iron oxide particles wherein the hydroxides and/or oxides of aluminum and/or silicon coat is disposed between the surface of said iron oxide particles and coating layer comprising said organosilicon compound according to the fourth aspect of the present invention is substantially the same in particle size, geometrical standard deviation value, BET specific surface area value, hue (a* value and b* value), desorption percentage of organic blue-based pigment, heat resistance, light resistance xcex94E1* value and acid resistance xcex94E2* value as those of the black composite iron oxide pigment produced by using the iron oxide particles having the hydroxides and/or oxides of aluminum and/or silicon coat as core particles according to the second aspect of the present invention, and is substantially the same in blackness as that of the black composite iron oxide pigment produced by using as core particles, the composite iron oxide particles precursor produced from the iron oxide particles having no hydroxides and/or oxides of aluminum and/or silicon coat according to the third aspect of the present invention.
Next, the paint containing the black composite iron oxide pigment according to the present invention will be described.
The coating film formed from a solvent-based paint containing the black composite iron oxide pigment according to the first aspect of the present invention has a gloss of usually not less than 75.0%, preferably not less than 80.0%, an acid resistance (xcex94G value) of usually not more than 10.0, preferably not more than 9.5, a light resistance (xcex94E3* value) of usually not more than 5.0, preferably not more than 4.5, and a heat resistance (heat-resisting temperature) of not less than 300xc2x0 C., preferably not less than 305xc2x0 C. As to the hue of the coating film, the L* value thereof is usually 16.0 to 23.0, preferably 16.0 to 22.0, more preferably 16.0 to 21.0; the a* value thereof is usually xe2x88x922.0 to 0.0, preferably xe2x88x922.0 to xe2x88x920.1, more preferably xe2x88x922.0 to xe2x88x920.2; and the b* value thereof is usually xe2x88x926.5 to 1.5, preferably xe2x88x926.5 to 1.0.
The coating film formed from a solvent-based paint containing the black composite iron oxide pigment according to the second aspect of the present invention has a gloss of usually not less than 80.0%, preferably not less than 850.0%, an acid resistance (xcex94G value) of usually not more than 9.5, preferably not more than 9.0, a light resistance (xcex94E3* value) of usually not more than 4.5, preferably not more than 4.0, and a heat resistance (heat-resisting temperature) of not less than 305xc2x0 C., preferably not less than 310xc2x0 C. As to the hue of the coating film, the L* value thereof is usually 16.0 to 23.0, preferably 16.0 to 22.0, more preferably 16.0 to 21.0; the a* value thereof is usually xe2x88x922.0 to 0.0, preferably xe2x88x922.0 to xe2x88x920.1, more preferably xe2x88x922.0 to xe2x88x920.2; and the b* value thereof is usually xe2x88x926.5 to 1.5, preferably xe2x88x926.5 to 1.0.
The coating film formed from a solvent-based paint containing the black composite iron oxide pigment according to the third aspect of the present invention has a gloss of usually not less than 80.0%, preferably not less than 85.0%, an acid resistance (xcex94G value) of usually not more than 9.0, preferably not more than 8.5, a light resistance (xcex94E3* value) of usually not more than 4.5, preferably not more than 4.0, and a heat resistance (heat-resisting temperature) of not less than 305xc2x0 C., preferably not less than 3105xc2x0 C. As to the hue of the coating film, the L* value thereof is usually 14.5 to 21.0, preferably 14.5 to 20.0, more preferably 14.5 to 19.0; the a* value thereof is usually xe2x88x922.0 to 0.0, preferably xe2x88x922.0 to xe2x88x920.1, more preferably xe2x88x922.0 to xe2x88x920.2; and the b* value thereof is usually xe2x88x926.5 to 1.5, preferably xe2x88x926.5 to 1.0.
The coating film formed from a solvent-based paint containing the black composite iron oxide pigment according to the fourth aspect of the present invention has a gloss of usually not less than 85.0%, preferably not less than 90.0%, an acid resistance (xcex94G value) of usually not more than 8.5, preferably not more than 8.0, a light resistance (xcex94E3* value) of usually not more than 4.0, preferably not more than 3.5, and a heat resistance (heat-resisting temperature) of not less than 310xc2x0 C., preferably not less than 315xc2x0 C. As to the hue of the coating film, the L* value thereof is usually 14.5 to 21.0, preferably 14.5 to 20.0, more preferably 14.5 to 19.0; the a* value thereof is usually xe2x88x922.0 to 0.0, preferably xe2x88x922.0 to xe2x88x920.1, more preferably xe2x88x922.0 to xe2x88x920.2; and the b* value thereof is usually xe2x88x926.5 to 1.5, preferably xe2x88x926.5 to 1.0.
The coating film formed from a water-based paint containing the black composite iron oxide pigment according to the first aspect of the present invention has a gloss of usually not less than 70.0%, preferably not less than 75.0%, an acid resistance (xcex94G value) of usually not more than 10.0, preferably not more than 9.5, a light resistance (xcex94E3* value) of usually not more than 5.0, preferably not more than 4.5, and a heat resistance (heat-resisting temperature) of not less than 300xc2x0 C., preferably not less than 305xc2x0 C. As to the hue of the coating film, the L* value thereof is usually 16.0 to 23.0, preferably 16.0 to 22.0, more preferably 16.0 to 21.0; the a* value thereof is usually xe2x88x922.0 to 0.0, preferably xe2x88x922.0 to xe2x88x920.1, more preferably xe2x88x922.0 to xe2x88x920.2; and the b* value thereof is usually xe2x88x926.5 to 1.5, preferably xe2x88x926.5 to 1.0.
The coating film formed from a water-based paint containing the black composite iron oxide pigment according to the second aspect of the present invention has a gloss of usually not less than 75.0%, preferably not less than 80.0%, an acid resistance (xcex94G value) of usually not more than 9.5, preferably not more than 9.0, a light resistance (xcex94E3* value) of usually not more than 4.5, preferably not more than 4.0, and a heat resistance (heat-resisting temperature) of not less than 305xc2x0 C., preferably not less than 310xc2x0 C. As to the hue of the coating film, the L* value thereof is usually 16.0 to 23.0, preferably 16.0 to 22.0, more preferably 16.0 to 21.0; the a* value thereof is usually xe2x88x922.0 to 0.0, preferably xe2x88x922.0 to xe2x88x920.1, more preferably xe2x88x922.0 to xe2x88x920.2; and the b* value thereof is usually xe2x88x926.5 to 1.5, preferably xe2x88x926.5 to 1.0.
The coating film formed from a water-based paint containing the black composite iron oxide pigment according to the third aspect of the present invention has a gloss of usually not less than 75.0%, preferably not less than 80.0%, an acid resistance (xcex94G value) of usually not more than 9.0, preferably not more than 8.5, a light resistance (xcex94E3* value) of usually not more than 4.5, preferably not more than 4.0, and a heat resistance (heat-resisting temperature) of not less than 305xc2x0 C., preferably not less than 310xc2x0 C. As to the hue of the coating film, the L* value thereof is usually 14.5 to 21.0, preferably 14.5 to 20.0, more preferably 14.5 to 19.0; the a* value thereof is usually xe2x88x922.0 to 0.0, preferably xe2x88x922.0 to xe2x88x920.1, more preferably xe2x88x922.0 to xe2x88x920.2; and the b* value thereof is usually xe2x88x926.5 to 1.5, preferably xe2x88x926.5 to 1.0.
The coating film formed from a water-based paint containing the black composite iron oxide pigment according to the fourth aspect of the present invention has a gloss of usually not less than 80.0%, preferably not less than 85.0%, an acid resistance (xcex94G value) of usually not more than 8.5, preferably not more than 8.0, a light resistance (xcex94E3* value) of usually not more than 4.0, preferably not more than 3.5, and a heat resistance (heat-resisting temperature) of not less than 310xc2x0 C., preferably not less than 315xc2x0 C. As to the hue of the coating film, the L* value thereof is usually 14.5 to 21.0, preferably 14.5 to 20.0, more preferably 14.5 to 19.0; the a* value thereof is usually xe2x88x922.0 to 0.0, preferably xe2x88x922.0 to xe2x88x920.1, more preferably xe2x88x922.0 to xe2x88x920.2; and the b* value thereof is usually xe2x88x926.5 to 1.5, preferably xe2x88x926.5 to 1.0.
The amount of the black composite iron oxide pigment blended in the paint according to the present invention is 1.0 to 100 parts by weight based on 100 parts by weight of a paint base material. In the consideration of handling property of the paint, the amount of the black composite iron oxide pigment blended in the paint is preferably 2.0 to 100 parts by weight, more preferably 5.0 to 100 parts by weight based on 100 parts by weight of the paint base material.
The paint base material comprises a resin and a solvent, and may further contain, if required, a defoamer, an extender pigment, a drying promoter, a surfactant, a curing accelerator, assistants or the like.
Examples of the resin used in the paint base material for solvent-based paints may include those ordinarily used for solvent-based paints such as acrylic resins, alkyd resins, polyester resins, polyurethane resins, epoxy resins, phenol resins, melamine resins and amino resins. Examples of the resins used in the paint base material for water-based paints may include those ordinarily used for water-based paints such as water-soluble alkyd resins, water-soluble melamine resins, water-soluble acrylic resins and water-soluble urethane emulsion resins.
As the solvent for solvent-based paints, there may be exemplified those solvents ordinarily used for solvent-based paints such as toluene, xylene, butyl acetate, methyl acetate, methyl isobutyl ketone, butyl cellosolve, ethyl cellosolve, butyl alcohol and aliphatic hydrocarbons.
As the solvents for water-based paints, there may be exemplified those solvents ordinarily used in combination with water for water-based paints, such as butyl cellosolve and butyl alcohol.
As the defoamer, there may be used commercially available products such as xe2x80x9cNOPCO 8034 (tradename)xe2x80x9d, xe2x80x9cSN DEFOAMER 477 (tradename)xe2x80x9d, xe2x80x9cSN DEFOAMER 5013 (tradename)xe2x80x9d, xe2x80x9cSN DEFOAMER 247 (tradename)xe2x80x9d and xe2x80x9cSN DEFOAMER 382 (tradename)xe2x80x9d (all produced by SUN NOPCO CO., LTD.), xe2x80x9cANTI-FOAM 08 (tradename)xe2x80x9d and xe2x80x9cEMARGEN 903 (tradename)xe2x80x9d (both produced by KAO CO., LTD.), or the like.
Next, the resin composition tinted with the black composite iron oxide pigment according to the present invention is described.
The resin composition tinted with the black composite iron oxide pigment according to the first aspect of the present invention exhibits a dispersing condition of the rank 4 or 5 when visually observed by the below-mentioned evaluation method, a heat resistance (heat-resisting temperature) of usually not less than 225xc2x0 C., preferably not less than 230xc2x0 C., and a light resistance (xcex94E5* value) of usually not more than 5.0, preferably not more than 4.5. As to the hue of the resin composition, the L* value thereof is usually 16.0 to 23.5, preferably 16.0 to 22.5, more preferably 16.0 to 21.5; the a* value thereof is usually xe2x88x922.0 to 0.0, preferably xe2x88x922.0 to xe2x88x920.1, more preferably xe2x88x922.0 to xe2x88x920.2; and the b* value thereof is usually xe2x88x926.5 to 1.5, preferably xe2x88x926.5 to 1.0.
The resin composition tinted with the black composite iron oxide pigment according to the second aspect of the present invention exhibits a dispersing condition of the rank 4 or 5 when visually observed by the below-mentioned evaluation method, a heat resistance (heat-resisting temperature) of usually not less than 230xc2x0 C., preferably not less than 235xc2x0 C., and a light resistance (xcex94E5* value) of usually not more than 4.5, preferably not more than 4.0. As to the hue of the resin composition, the L* value thereof is usually 16.0 to 23.5, preferably 16.0 to 22.5, more preferably 16.0 to 21.5; the a* value thereof is usually xe2x88x922.0 to 0.0, preferably xe2x88x922.0 to xe2x88x920.1, more preferably xe2x88x922.0 to xe2x88x920.2; and the b* value thereof is usually xe2x88x926.5 to 1.5, preferably xe2x88x926.5 to 1.0.
The resin composition tinted with the black composite iron oxide pigment according to the third aspect of the present invention exhibits a dispersing condition of the rank 4 or 5 when visually observed by the below-mentioned evaluation method, a heat resistance (heat-resisting temperature) of usually not less than 230xc2x0 C., preferably not less than 235xc2x0 C., and a light resistance (xcex94E5* value) of usually not more than 4.5, preferably not more than 4.0. As to the hue of the resin composition, the L* value thereof is usually 14.5 to 21.5, preferably 14.5 to 20.5, more preferably 14.5 to 19.5; the a* value thereof is usually xe2x88x922.0 to 0.0, preferably xe2x88x922.0 to xe2x88x920.1, more preferably xe2x88x922.0 to xe2x88x920.2; and the b* value thereof is usually xe2x88x926.5 to 1.5, preferably xe2x88x926.5 to 1.0.
The resin composition tinted with the black composite iron oxide pigment according to the fourth aspect of the present invention exhibits a dispersing condition of the rank 4 or 5 when visually observed by the below-mentioned evaluation method, a heat resistance (heat-resisting temperature) of usually not less than 235xc2x0 C., preferably not less than 240xc2x0 C., and a light resistance (xcex94E5* value) of usually not more than 4.0, preferably not more than 3.5. As to the hue of the resin composition, the L* value thereof is usually 14.5 to 21.5, preferably 14.5 to 20.5, more preferably 14.5 to 19.5; the a* value thereof is usually xe2x88x922.0 to 0.0, preferably xe2x88x922.0 to xe2x88x920.1, more preferably xe2x88x922.0 to xe2x88x920.2; and the b* value thereof is usually xe2x88x926.5 to 1.5, preferably xe2x88x926.5 to 1.0.
The amount of the black composite iron oxide pigment blended in the resin composition according to the present invention is 0.5 to 200 parts by weight based on 100 parts by weight of a base material of the resin composition. In the consideration of handling property of the resin composition, the amount of the black composite iron oxide pigment blended therein is preferably 1.0 to 150 parts by weight, more preferably 2.5 to 100 parts by weight based on 100 parts by weight of the base material.
The base material of the resin composition according to the present invention comprises the black composite iron oxide pigment and known thermoplastic resins, and may further contain, if required, additives such as lubricants, plasticizers, antioxidants, ultraviolet light absorbers, various stabilizers or the like.
Examples of the reins may include natural rubbers, synthetic rubbers, thermoplastic resins, e.g., polyolefins such as polyethylene, polypropylene, polybutene and polyisobutylene, polyvinyl chloride, styrene polymers and polyamides, or the like.
The additive may be added in an amount of usually not more than 50% by weight based on the total amount of the black composite iron oxide pigment and the resin. When the amount of the additive added is more than 50% by weight, the obtained resin composition is deteriorated in moldability.
The resin composition of the present invention can be produced by previously intimately mixing the raw resin material with the black composite iron oxide pigment, and then kneading the resultant mixture using a kneader or an extruder under heating while applying a strong shear force thereto in order to deaggregate the agglomerated black composite iron oxide pigment and uniformly disperse the black composite iron oxide pigment in the resin. Then, the obtained resin composition is molded into an aimed shape upon use.
Next, the process for producing the black composite iron oxide pigment according to the present invention is described.
The granular magnetite particles used as the core particles in the present invention can be produced by a so-called wet-method of passing an oxygen-containing gas through a suspension containing a ferrous hydroxide colloid obtained by reacting an aqueous ferrous salt solution with alkali hydroxide, for conducting the oxidation reaction.
The granular manganese-containing hematite particles used as the core particles in the present invention can be produced by heat-treating either (i) particles obtained by coating the granular magnetite particles produced by the above wet method with a manganese compound in an amount of usually 8 to 150 atm % based on whole Fe, or (ii) manganese-containing magnetite particles obtained by conducting the above wet method for the production of granular magnetite particles in the presence of manganese to produce magnetite particles containing manganese in an amount of usually 8 to 150 atm % based on whole Fe and then subjecting the obtained magnetite particles to filtration, water-washing and drying, at a temperature of usually 750 to 1000xc2x0 C. in air.
The thus obtained manganese-containing hematite particles are preferred from the standpoint of dispersibility since these particles are non-magnetic particles and, therefore, can be prevented from being magnetically agglomerated together.
The black composite iron oxide pigment of the present invention can be produced by mixing the iron oxide particles as core particles with alkoxysilanes or polysiloxanes to coat the surface of the iron oxide particles with the alkoxysilanes or polysiloxanes, and then mixing the thus obtained iron oxide particles coated with the alkoxysilanes or polysiloxanes with the organic blue-based pigment.
The coating of the iron oxide particles (A), or the composite iron oxide particles precursor (B) as core particles with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, or the terminal-modified polysiloxanes, may be conducted (i) by mechanically mixing and stirring the iron oxide particles (A), or the composite iron oxide particles precursor (B) together with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, or the terminal-modified polysiloxanes; or (ii) by mechanically mixing and stirring both the components together while spraying the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, or the terminal-modified polysiloxanes onto the core particles. In these cases, substantially whole amount of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, or the terminal-modified polysiloxanes added can be applied onto the surfaces of the core particles.
In addition, by conducting the above-mentioned mixing or stirring treatment (i) of the iron oxide particles (A), or the composite iron oxide particles precursor (B) as core particles together with the alkoxysilane compounds, at least a part of the alkoxysilane compounds coated on the core particles may be changed to the organosilane compounds. In this case, there is also no affection against the formation of the organic blue-based pigment coat thereon.
In order to uniformly coat the surfaces of the iron oxide particles (A), or the composite iron oxide particles precursor (B) as core particles with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, or the terminal-modified polysiloxanes, it is preferred that the iron oxide particles (A) or the composite iron oxide particles precursor (B) are preliminarily diaggregated by using a pulverizer.
As apparatus (a) for mixing and stirring treatment (i) of the core particles with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, or the terminal-modified polysiloxanes to form the coating layer thereof, and as apparatus (b) for mixing and stirring treatment (ii) of the organic blue-based pigment with the core particles whose surfaces are coated with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, or the terminal-modified polysiloxanes to form the organic blue-based pigment coat, there may be preferably used those apparatus capable of applying a shear force to the particles, more preferably those apparatuses capable of conducting the application of shear force, spaturate force and compressed force at the same time.
As such apparatuses, there may be exemplified wheel-type kneaders, ball-type kneaders, blade-type kneaders, roll-type kneaders or the like. Among them, wheel-type kneaders are preferred.
Specific examples of the wheel-type kneaders may include an edge runner (equal to a mix muller, a Simpson mill or a sand mill), a multi-mull, a Stotz mill, a wet pan mill, a Conner mill, a ring muller, or the like. Among them, an edge runner, a multi-mull, a Stotz mill, a wet pan mill and a ring muller are preferred, and an edge runner is more preferred.
Specific examples of the ball-type kneaders may include a vibrating mill or the like. Specific examples of the blade-type kneaders may include a Henschel mixer, a planetary mixer, a Nawter mixer or the like. Specific examples of the roll-type kneaders may include an extruder or the like.
In order to coat the surfaces of the core particles with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, or the terminal-modified polysiloxanes as uniformly as possible, the conditions of the above mixing or stirring treatment may be appropriately controlled such that the linear load is usually 19.6 to 1960 N/cm (2 to 200 Kg/cm), preferably 98 to 1470 N/cm (10 to 150 Kg/cm), more preferably 147 to 980 N/cm (15 to 100 Kg/cm); and the treating time is usually 5 to 120 minutes, preferably 10 to 90 minutes. It is preferred to appropriately adjust the stirring speed in the range of usually 2 to 2,000 rpm, preferably 5 to 1,000 rpm, more preferably 10 to 800 rpm.
The amount of the alkoxysilanes or polysiloxanes added is usually 0.15 to 45 parts by weight based on 100 parts by weight of the iron oxide particles. When the amount of the alkoxysilanes or polysiloxanes added is less than 0.15 part by weight, it may become difficult to adhere the organic blue-based pigment in such an amount sufficient to improve a blackness of the obtained pigment. When the alkoxysilanes or polysiloxanes are added in an amount of 0.15 to 45 parts by weight, it is possible to adhere a sufficient amount of the organic blue-based pigment onto the iron oxide particles. Therefore, it is unnecessary and meaningless to add the alkoxysilanes or polysiloxanes in an amount of more than 45 parts by weight.
Next, the organic blue-based pigment are added to the iron oxide particles (A), or the composite iron oxide particles precursor (B) as core particles, which are coated with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, or the terminal-modified polysiloxanes, and the resultant mixture is mixed and stirred to form the organic blue-based pigment coat on the surfaces of the coating layer composed of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes. The drying or heat-treatment may be conducted.
It is preferred that the organic blue-based pigment are added little by little and slowly, especially about 5 to 60 minutes.
In order to form organic blue-based pigment coat onto the coating layer composed of the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes, or the terminal-modified polysiloxanes as uniformly as possible, the conditions of the above mixing or stirring treatment can be appropriately controlled such that the linear load is usually 19.6 to 1960 N/cm (2 to 200 Kg/cm), preferably 98 to 1470 N/cm (10 to 150 Kg/cm), more preferably 147 to 980 N/cm (15 to 100 Kg/cm); and the treating time is usually 5 to 120 minutes, preferably 10 to 90 minutes. It is preferred to appropriately adjust the stirring speed in the range of usually 2 to 2,000 rpm, preferably 5 to 1,000 rpm, more preferably 10 to 800 rpm.
The amount of the organic blue-based pigment added is usually 1 to 50 parts by weight based on 100 parts by weight of the iron oxide particles. When the amount of the organic blue-based pigment added is less than 1 part by weight, the amount of the organic blue-based pigment adhered may be insufficient, thereby failing to exhibit a deep black color.
By adhering 1 to 50 parts by weight of the organic blue-based pigment, the black composite iron oxide pigment showing a deep black color, and excellent light resistance and acid resistance, which is an objective pigment of the present invention, can be obtained
In case of drying the obtained composite iron oxide particles, the temperature is usually 40 to 200xc2x0 C., preferably 60 to 150xc2x0 C. The treating time of these steps is usually from 10 minutes to 12 hours, preferably from 30 minutes to 3 hours.
When the obtained composite iron oxide particles is subjected to the above step, the alkoxysilane compounds used as the coating thereof are finally converted into organosilane compounds.
If required, prior to mixing and stirring with the alkoxysilane compounds or polysiloxanes, the iron oxide particles may be preliminarily coated with at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon to form an hydroxides and/or oxides of aluminum and/or silicon coat thereon.
At least a part of the surface of the iron oxide particles may be coated with at least one compound selected from the group consisting of hydroxides and/or oxides of aluminum and/or silicon, if required, in advance of mixing and stirring with the alkoxysilane compounds, the polysiloxanes, the modified polysiloxanes or the terminal-modified polysiloxanes.
The coat of the hydroxides and/or oxides of aluminum and/or silicon may be conducted by adding an aluminum compound, a silicon compound or both the compounds to a water suspension in which the iron oxide particles are dispersed, followed by mixing and stirring, and further adjusting the pH value of the suspension, if required, thereby coating the surfaces of the iron oxide particles with hydroxides and/or oxides of aluminum and/or silicon. The thus obtained iron oxide particles coated with the hydroxides and/or oxides of aluminum and/or silicon are then filtered out, washed with water, dried and pulverized. Further, the iron oxide particles coated with the hydroxides and/or oxides of aluminum and/or silicon may be subjected to post-treatments such as deaeration treatment and compaction treatment, if required.
As the aluminum compounds, there may be exemplified aluminum salts such as aluminum acetate, aluminum sulfate, aluminum chloride or aluminum nitrate, alkali aluminates such as sodium aluminate or the like.
The amount of the aluminum compound added is 0.01 to 20% by weight (calculated as Al) based on the weight of the iron oxide particles. When the amount of the aluminum compound added is less than 0.01% by weight, it may be difficult to sufficiently coat the surfaces of the iron oxide particles with hydroxides and/or oxides of aluminum, thereby failing to improve the effective reduction of the organic blue-based pigment desorption percentage. On the other hand, when the amount of the aluminum compound added is more than 20% by weight, the coating effect is saturated and, therefore, it is meaningless to add such an excess amount of the aluminum compound.
As the silicon compounds, there may be exemplified #3 water glass, sodium orthosilicate, sodium metasilicate or the like.
The amount of the silicon compound added is 0.01 to 20% by weight (calculated as SiO2) based on the weight of the iron oxide particles.
In the case where both the aluminum and silicon compounds are used in combination for the coating, the total amount of the aluminum and silicon compounds added is preferably 0.01 to 20% by weight (calculated as a sum of Al and SiO2) based on the weight of the iron oxide particles.
The point of the present invention is that the black composite iron oxide pigment produced by adhering an organic blue-based pigment onto the surface of iron oxide particles through a coating layer comprising organosilicon compounds can exhibit not only a deep black color, but also excellent acid resistance and light resistance.
The reason why the black composite iron oxide pigment of the present invention can exhibit a deep black color is considered as follows, though not clearly determined. That is, by selectively using the organic blue-based pigment for reducing a reddish color of iron oxide particles, and using the organosilicon compounds such as alkoxysilanes or polysiloxanes as a gluing agent for strongly adhering the organic blue-based pigment onto the surface of the iron oxide particles, the a* value of the obtained black composite iron oxide pigment as an index representing a reddish color thereof can be reduced to not more than 0.
The reason why the black composite iron oxide pigment of the present invention can exhibit an excellent acid resistance is considered by the present inventors as follows. That is, since the organic blue-based pigment having an excellent acid resistance is adhered onto the surface of the iron oxide particles through a coating layer comprising organosilane compounds obtainable from alkoxysilanes, or polysiloxanes, it is possible to shield inherent properties of the iron oxide particles such as oxidation susceptibility and high surface activity, thereby more effectively exhibiting inherent properties of the organic blue-based pigment.
The reason why the black composite iron oxide pigment of the present invention can exhibit an excellent light resistance is considered by the present inventors as follows. That is, since the iron oxide particles inherently showing a poor light resistance is covered with the coating layer comprising the organosilicon compounds such as organosilane compounds or polysiloxanes having an excellent light resistance, and further the organic blue-based pigment having an excellent light resistance is adhered on the coating layer, the obtained black composite iron oxide pigment can be considerably improved in light resistance.
The reason why the amount of the organic blue-based pigment desorbed from the surface of the black composite iron oxide pigment of the present invention is reduced, is considered by the present inventors as follows. That is, metalloxane bonds (xe2x89xa1Sixe2x80x94Oxe2x80x94M, wherein M represents a metal atom contained in the iron oxide particle, such as Si, Al or Fe) are formed between the metal elements such as Si, Al or Fe which are contained within the iron oxide particle or present at the surface thereof, and alkoxy groups of the alkoxysilane compounds, so that the organosilicon compounds onto which the organic blue-based pigment is adhered, can be more strongly bonded to the surface of the iron oxide particle.
The reason why the black composite iron oxide pigment of the present invention can exhibit an excellent dispersibility in vehicles or resin compositions, is considered by the present inventors as follows. That is, since the amount of the organic blue-based pigment desorbed from the surface of the black composite iron oxide pigment is small, the black composite iron oxide pigment can be dispersed in the vehicles or resin compositions without disturbance by the desorbed organic blue-based pigment. In addition, since the organic blue-based pigment is adhered onto the surface of the black composite iron oxide pigment, irregularities are formed on the surface of the respective pigment particles, thereby effectively preventing the contact between the particles.
Also, the black composite iron oxide pigment according to the third aspect of the present invention can show an excellent blackness because carbon black is adhered onto the surface of the iron oxide particles though a coating layer comprising the organosilicon compound such as organosilane compounds obtainable from alkoxysilanes, or polysiloxanes.
The paint and resin composition of the present invention contain such a black composite iron oxide pigment and, therefore, can exhibit excellent light resistance and acid resistance.
The black composite iron oxide pigment of the present invention can exhibit not only a deep black color but also excellent acid resistance and light resistance and, therefore, is suitably used as a black pigment.
Further, the paint and resin composition of the present invention can exhibit excellent light resistance, heat resistance and acid resistance, and is prepared using the harmless black composite iron oxide pigment. Therefore, the paint and resin composition can be suitably used as black paints and resin compositions which are free from environmental pollution.